The invention is directed to an improved visual field testing device which enables a human operator to perform visual field tests faster and more reliably than heretofore possible with conventional human-operated devices.
Visual field tests are important tools of the ophthalmologist for detecting numerous diseases and defects of the eye, optic nerve and brain. In simplest form, a visual field test is conducted by sequentially displaying a series of individual light targets on a screen and noting those targets which can be seen by a patient whose eye is fixated on the center of the screen. The targets which the patient can see define the patient's visual field. Targets which the patient cannot see can be used to determine defects within the visual field. In kinetic perimetry tests, a light target is moved along a path from the outside of the patient's visual field until the patient responds to the stimulus. In static perimetry tests, the light targets are fixed points which do not move. Instead, the size and/or intensity may be increased until the patient responds to the stimulus.
Numerous devices have been designed to test visual fields. For example, U.S. Pat. No. 3,421,498 discloses a device comprised of a screen containing a plurality of apertures through which lights are sequentially shown. As the lights appear, the patient acknowledges vision by pressing a hand held button or switch. The response is automatically noted on a visual fiedl chart by a recorder. If the patient fails to see a light he does not respond and this is apparent on the chart.
Because this type of visual field tester utilizes a screen containing fixed lamps, it is not possible to conduct a highly detailed test of a section of the patient's visual field in the area between two adjacent lamps. In view of this shortcoming, many current visual field testing devices do not use screens containing fixed lamps but contain means for projecting an individual light target at any point on the screen.
Thus, in perhaps the best known visual field testing device, often referred to as a Goldmann perimeter, the operator positions a marker at a particular point on a visual field chart. The marker is connected to a light source by a lever arrangement which positions the source such that light is directed onto the screen corresponding to the point of location of the marker on the visual field chart. Because there are no fixed lamps, an infinite number of points within the visual field can be tested. However, it is often quite difficult to position the light source due to drifting and general instability of the lever connecting the light sources to the marker.
More recently, in U.S. Pat. No. 4,260,227, a device is disclosed which conducts visual field tests automatically. This device utilizes a stationary source of light which projects light onto a mirror which reflects it onto the screen. The mirror is rotatable along its axis and around the circumference of the perimeter bowl. By rotating the mirror around the circumference of the bowl and adjusting the angle of the mirror, the light can be directed to any point on the screen. The mirror is controlled by a servo-mechanism which is connected to a mini-computer which is programmed to sequentially adjust the position of the mirror through the servo-mechanism and to receive and record the responses of the patient.
However, because this device is fully automated, it cannot be used by an ophthalmologist to conduct an individualized visual field test. This is particularly important when the ophthalmologist is relying upon the test to aid him in planning a clinical or surgical R.sub.x.